The present invention relates generally to semiconductor fabrication and, more specifically, to performing multiple wafer processing operations in a single wafer processing module using replaceable pad assemblies.
Fabrication of semiconductor devices involves wafer preparation and cleaning operations. Chemical mechanical planarization (CMP) operation is one of the wafer preparation operations designed to achieve global and local planarization of a wafer surface. Typically, the planarization of a wafer involves multiple CMP operations wherein various layers formed over the substrate surface are polished and planarized. A CMP system usually includes system components for handling and polishing the surface of a wafer. Such components can be, for example, a rotary polishing pad, an orbital polishing pad, or a linear belt polishing pad.
Generally, each different CMP operation requires specific consumables (e.g., polishing pad, slurry, etc.). A polishing pad, however, is attached to a polishing table in an orbital or rotary polishing pad. Thus, typical orbital or rotary CMP systems are considered to have rigid and inflexible configurations because the pad has to be ripped off of the polishing table causing polishing pad removal to be a labor intensive and time consuming task.
FIG. 1 is a simplified schematic diagram of a prior art wafer preparation and cleaning system. The system includes a wafer cassette 2 that holds unprocessed wafers, a plurality of modules 7–9 designed to perform different CMP operations, post CMP modules 6, and a wafer cassette 4 designed to receive and hold processed wafers. Each of the modules 7–9 performs different CMP operations in parallel. After each and every operation has completed, wafers are consecutively and simultaneously moved from the module 7, to the module 8, and from module 8 to module 9.
In FIG. 1, the module 7 performs a bulk removal CMP operation using a pad and slurry associated with the bulk removal CMP operation, module 8 performs the barrier removal using a pad and slurry associated with barrier removal, and the module 9 performs the buffing operation using a pad and slurry associated with the buffing operation. In short, usually, the pad materials and slurries are different depending on the CMP operation.
One shortcoming of the configuration shown in FIG. 1 is that because wafers should be transferred from one module to the next module simultaneously. In this manner, except in the slowest module, wafer processing in the remaining modules has to be elongated artificially. However, unless damage preventive measures are taken, artificially elongating wafer processing can result in corrosion and defective chips and thus wafer.
For instance, in the system shown in FIG. 1, each of the modules 7–9 can be programmed to process a corresponding wafer for one (1) minute. In this manner, performing all three CMP operations can take up to three (3) minutes. However, in operation, module 7 may require 20 seconds to conduct the first CMP operation, module 8 requires 35 seconds to conduct the second CMP operation, and module 9 requires 50 seconds to conduct the third CMP operation. As a consequence, in operation, modules 7–9 are required to artificially elongate respective operations up to 50 seconds, the time required by the module 9 (e.g., the slowest module) to complete processing the wafer. As a consequence, three CMP operations which should have been conducted in 105 seconds, unnecessarily take about 150 seconds, with a needless delay of 45 (30+15) seconds.
Still further, CMP operations may have to be interrupted so that unqualified consumables can be changed. Halting the CMP tool and operation is undesirable because problems usually follow a discontinuity or change of consumables in the CMP operation.
In view of the foregoing, there is a need for a flexible single module apparatus capable of optimizing performance of multiple operations.